1. Field of the Invention
The invention relates to a sheet bending machine of the type wherein the bending of a sheet of metal is performed by swinging a bending beam against a projecting part of the sheet metal fixed between a lower beam and a clamping beam. Such a sheet bending machine is e.g. described in DE-AS No. 1 076 608. The bending beam can be driven by electromotors or it can be moved hydraulically.
2. Description of Background Art
To be able to make various bendings, the clamping beam is usually provided with interchangeable folding rails with profiles permitting sharp bendings of e.g. 135.degree. or profiles permitting a rounded bending of up to 180.degree. which means that the bending beam also must be able to be swung or curved 180.degree..
To be able to adjust the bending angle in accordance with a certain working plan, the sheet bending machines are usually provided with members which can be programmed to switch off the current to the driving motors or to stop the supply of liquid to the hydraulic punch operating the bending beam. These members can as proposed in the above mentioned publication consist of discs or rolls with manually adjustable protrusion of cams which co-operate with contact rails so that being moved a length by the bending beam corresponding to a desired angle they actuate an electrical switch. For every working operation said discs or rolls are turned a step, so that the new protrusion activates the switching off of the movement of the bending beam. The angle movement of the bending beam can naturally also be operated electronically. Electronical operation on angle movements after an input program is well known and is not going to be described more closely.
Whether the input of the bending machine is performed in one way or another, it may be necessary to switch the program operation off. If after having switched off the automatical operation, the machine is unintentionally adjusted to a bending curve which is greater than the folding rail permits, it can result in damage to the machine. The same thing may take place if the input program and the folding rail used do not correspond. The object of the invention is to indicate such operating members for a sheet bending machine that is secured against fault programming as well as fault operation, so that curving of the bending beam beyond the angle a given folding rail permits is not possible.